DE10221793C1 - Non-grain oriented electrical steel or sheet and process for its manufacture - Google Patents

Abstract

The invention relates to non-grain-oriented electrical sheets which can be produced both as final-annealed and as non-final-annealed grades without additional manufacturing outlay in such a way that they have improved magnetic polarization and reduced magnetic reversal losses compared to the values which could previously be achieved. This is achieved in that a suitably assembled steel, when cooled, starting from an initial temperature of at most 1300 ° C., with essentially complete exclusion of a purely austenitic structure (gamma phase), passes through a temperature range in which it contains an austenite / Ferrite two-phase mixed structure (alpha, gamma mixed phases), so that the electrical sheet after hot rolling, pickling, cold rolling and annealing of the hot strip obtained after hot rolling has a magnetic measured in the longitudinal direction of the strip or sheet at a magnetic field strength of 2500 A / m Polarization J¶2500¶> = 1.74 T and a value p¶1.5¶ (50) of the magnetic losses of <4.5 measured in the longitudinal direction of the band at J = 1.5 T and a frequency f = 50 Hz W / kg.

Description

The invention relates to a non-grain oriented Electrical sheet or strip and a manufacturing process of such products.

Under the term "non-grain oriented electrical sheet" are here under DIN EN 10106 ("final annealed Electrical sheet ") and DIN EN 10165 (" not finally annealed Electrical sheet ") understood falling electrical sheets more anisotropic varieties are also included, as long as they are not considered grain-oriented electrical sheets. In this respect, the terms "electrical sheet" and "Electrical steel" used synonymously.

"J2500" and "J5000" in the following denote the magnetic polarization at a magnetic field strength of 2500 A / m or 5000 A / m. Under "P1.5" the Magnetic loss at a polarization of 1.5 T. and a frequency of 50 Hz understood.

The manufacturing industry makes the demand provided, not grain-oriented electrical sheets to compare their magnetic polarization values conventional sheets are raised. this applies especially for the area of applications where the electrical machines are electrically excited. Through the Magnetic polarization increases  Magnetization requirement reduced. Go along with it also the copper losses, which with a large number of electrical machines make up a significant part of the losses arising from the operation of electrical machines to have.

The economic value of not grain-oriented Electrical sheets with increased permeability are considerable. Electrical machines with electrical excitation, especially Industrial drives with powers that range from 1 kW to 100 kW Beyond that, the main area of application of non-grain oriented electrical sheet.

The demand for more permeable non-grain-oriented Electrical sheet types do not only affect non-grain-oriented ones Electrical sheets with high losses (P1.5 ≧ 5-6 W / kg), but also sheets with medium (3.5 W / kg ≦ P1.5 ≦ 5.5 W / kg) and low losses (P1.5 ≦ 3.5). Therefore one is strives to cover the full range of weak, medium and highly silicified electrotechnical steels with regard to to improve its magnetic polarization values. there have the electrical sheet types with Si contents of up to 2.5 mass% Si in terms of their market potential special meaning.

Intersee, in particular, has electrical sheet grades that have a high magnetic polarization value J ₂₅₀₀ or J _{5000 and} at the same time low magnetization loss values P _1.5 at 50 Hz, advantageously <4 W / kg, because they also reduce the magnetic excitation current in the case of electrically excited machines and a reduction in iron losses compared to conventional electrical sheet types with P _1.5 <4 W / kg at 50 Hz.

It is possible to reduce the magnetic losses by increasing the Si content. So pose Significantly reduced losses if the from the Si content and twice the total Al content formed % Si + 2% Al in for the production of electrical sheets in Steel in question used more than 1.4% is.

Various ways are known of how such high contents of Si and Al electrical sheets having high J ₂₅₀₀ or J ₅₀₀₀ can be achieved. It has been proposed in EP 0 651 061 A1 to achieve high degrees of deformation during cold rolling for this purpose, this cold rolling can be carried out in two stages with intermediate annealing. It is also known that higher-permeability types of electrical sheet can be produced by intermediate annealing of the hot strip (EP 0 469 980 B1, DE 40 05 807 C2). According to the method known from EP 0 431 502 A2, a non-grain-oriented electrical sheet is finally produced by using ≦ 0.025% C, <0.1% Mn, 0.1 to 4.4% Si and 0.1 to 4.4% Steel raw material containing Al (data in mass%) is first hot-rolled to a thickness of not less than 3.5 mm. The hot strip obtained in this way is then cold-rolled without recrystallizing intermediate annealing with a degree of deformation of at least 86% and subjected to an annealing treatment. The band produced according to the known method has a particularly high magnetic polarization of more than 1.7 T with a field strength J ₂₅₀₀ of 2500 A / m and low magnetic reversal losses.

In practice, however, it turns out that it is not possible with the known measures, with the security required for large-scale production, electrical sheets with a total content of more than 1.4 mass% of Si and Al non-grain-oriented electrical strips or sheets to produce, which have a magnetic polarization J ₂₅₀₀ of ≧ 1.7 T measured in the longitudinal direction of the tape. (The values determined for the J ₂₅₀₀ in the transverse direction of the belt and the mixed values of J ₂₅₀₀ are always smaller than the values of J ₂₅₀₀ measured in the belt direction.)

Improvements with regard to higher values of J ₂₅₀₀ can be achieved when using highly silicified alloys of very high purity, especially with a very low Si and Ti content and at the same time a very low C content. However, this route requires additional expenditure in steel production compared to the FeSi steels commonly used in practice.

The object of the invention was now based on the above-mentioned prior art high quality to produce non-grain-oriented electrical sheets that both as annealed and not annealed grades without additional manufacturing effort can be made to be one against the other previously achieved values improved magnetic Polarization and reduced magnetization losses exhibit.

This object is achieved according to the invention by a non-grain-oriented electrical steel sheet or sheet with a nominal thickness of ≦ 0.75 mm, made from a steel which, in addition to iron, contains the usual unavoidable levels of impurities (for example S, Ti) and optionally available levels of Mo, Sb, Sn , Zn, W and / or V, (in mass%) C: <0.005%, Mn: ≦ 1.0%, P: <0.8%, Al: <1% and Si with the requirement 1.4 Contains% <% Si + 2% Al <2.5% (with% Si = Si content and% Al = Al content), the steel thus assembled, with cooling, starting from a starting temperature of at most 1300 ° C. with restrictions of the temperature range in which an exclusively austenitic structure (γ phase) occurs in the steel during hot rolling, passes through a temperature range over a temperature range of less than 50 ° C. in which it has an austenite / ferrite two-phase mixture structure (α-, γ- Mixed phases), so that the electrical sheet after hot rolling, pickling, cold rolling en and annealing of the hot strip obtained after hot rolling, a magnetic polarization J ₂₅₀₀ ≧ 1.74 T measured in the longitudinal direction of the strip or sheet at a magnetic field strength of 2500 A / m and one in the longitudinal direction of the strip at J = 1.5 T and one Frequency f = 50 Hz measured value P _1.5 (50) of the magnetic losses of <4.5 W / kg.

The above-stated object is also achieved by a method for producing a non-grain-oriented electrical steel strip or sheet obtained according to one of the preceding claims, in which the following steps are carried out:

• - Pouring a steel next to iron, the usual inevitable levels of impurities (for example S, Ti) and optionally available Contained on Mo, Sb, Sn, Zn, W and / or V, (in mass%) C: <0.005%, Mn: ≦ 1.0%, P: <0.8%, Al: <1% as well Si with the requirement 1.4% <% Si + 2% Al <2.5% (with% Si = Si content and% Al = Al content) Intermediate product, such as a slab, a thin slab or a cast tape,  
• - Processing of the preliminary product into a hot strip in one Hot rolling process at hot rolling temperatures starting from from ≦ 1300 ° C so that under Essentially complete exclusion of a pure austenitic structure (γ phase) a temperature range is run through, in which the processed steel Austenite / ferrite two-phase mixed structure (α, γ mixed phases) and has a ferrite area,
• - so that the electrical steel strip or sheet after a surface treatment comprising pickling, cold rolling and annealing of the hot strip obtained after the hot rolling process has a magnetic polarization J ₂₅ ≧ 1 measured in the longitudinal direction of the strip or sheet at a magnetic field strength of 2500 A / m, 74 T and a value P _1.5 (50) of the magnetic losses of <4.5 W / kg measured in the longitudinal direction of the band at J = 1.5 T and a frequency f = 50 Hz,
• - with the span of the temperature range, within of which the processed steel is a purely austenitic Structure (γ phase) is less than 50 ° C, and being the temperatures during the hot rolling process bypassing this temperature range.

Surprisingly, it has been shown that the selection of a suitably composed steel alloy and the special temperature control during the hot processing of the preliminary product cast from this steel alloy can produce an electrical sheet that has significantly improved values of the magnetic losses and the magnetic permeability compared to the prior art. Thus, in the case of electrical sheets obtained according to the invention, a magnetic polarization J ₂₅₀₀ measured in the longitudinal direction of at least 1.74 T, in particular even at least 1.76 T, can be ensured. Magnetic losses P _1.5 of less than 4.5 W / kg, especially 4 W / kg, can also be guaranteed.

The prerequisite for this is that the one used according to the invention Steel is composed so that it is at a temperature of 1300 ° C outgoing cooling at no time if possible has a purely austenitic structure. Instead is to choose the composition so that when cooling necessary to go through a temperature area within whose steel structure consists of a mixture of γ- and α- Phases. As in the sense of the invention still There will be a tolerable deviation from this regulation viewed when pure austenite structure over a Temperature range of maximum 50 ° C occurs. This means, that if a pure austenite structure is formed, at the latest after a temperature decrease by another 50 ° C two-phase mixed structure must again be present.

It could be shown that at 50 ° C above Deviation beyond the temperature tolerance range through the invention achieved increase in the quality of Electrical sheets cannot be reached. Preferably are therefore according to the invention during manufacture Electrical bands managed the temperatures so that the critical temperature range is bypassed. This can for example the reheating temperature of the slab in the conventional hot strip manufacturing process or Thin slab temperature during casting or rolling Thin strip casting should be selected before hot rolling so that it lies above the two-phase area. The Final hot rolling temperature is <800 ° C.  

If the hot strip processing includes a reel, the should Coil temperature at which the hot strip is cut after Hot rolling process is <650 ° C.

If slabs or thin slabs of greater thickness are processed in the production of electrical sheets according to the invention, the hot rolling process usually comprises a final rolling (finished hot rolling) which takes place in a hot rolling mill comprising a plurality of roll stands. In order to produce particularly high-quality electrical sheets, the overall degree of forming achieved in the course of the final rolling should be <75%. Electrical sheets that have magnetic polarization J ₂₅₀₀ values of more than 1.74 T with particularly low losses P _1.5 of significantly less than 4 W / kg can be produced by the degree of deformation achieved in the course of the final rolling in the two-phase mixing area is at least 35%.

Electrical sheets with good according to the invention can also be used Establish properties when the hot rolled Pre-product before entering the hot rolling mill under Passage through the two-phase mixing area has cooled as far that the final rolling in hot rolling essentially at ferritic structure of the processed steel takes place.

It is preferred if the final rolling during Hot rolling in the ferritic state Steel is carried out, at least one of the last Forming stitches with hot-rolled lubrication. By the Hot rolling with lubrication occurs on the one hand less Shear deformations so that the rolled strip in Result a more homogeneous structure across the cross section receives. On the other hand, the lubrication Rolling forces are reduced, so that over the respective  Roll pass a higher thickness reduction is possible. Therefore it will be beneficial if everyone in the ferrite area forming stitches with roller lubrication be performed.

Improved surface properties according to the invention Electrical sheets can be achieved by that Hot strip in the course of its surface treatment before Pickling is descaled mechanically.

The final annealing of the cold rolled from the hot strip Electrical steel can basically in the run or in Hood furnace (final annealed electrical steel). Alternatively, the annealed strip can be run through after it or annealing carried out in a bell-type furnace with a Degree of deformation <12% post-formed and then one Subjected to reference annealing at temperatures above 700 ° C become a non-final annealed electrical steel is obtained.

The invention is described below with reference to Embodiments explained in more detail.

The attached diagram shows the phase diagram of one binary FeSi alloy. Analog diagrams apply to technical alloys, the respective "Temperatures" compared to those shown change binary alloy.

In the diagram, the areas in which there is a purely ferritic (α), a purely austenitic (γ) or a two-phase mixed structure (γ + α) formed from ferrite and austenite, depending on the respective temperature and that of the respective Si Content and twice the Al content of the steel processed in each case, the sum of "% Si + 2% Al". In addition, the lines L _U , L _O running parallel to the axis of the temperatures delimit the range within which the alloys selected according to the invention lie.

It can be seen that the line L _U marking the lower limit of the sum "% Si + 2% Al" of the Si and Al contents of alloys processed according to the invention over a temperature range T _s corresponds to the smaller amounts of the sum "% Si + 2 % Al "extends the austenite phase region γ in which pure austenite is formed. The temperature difference, which lies between the upper intersection T _so and the lower intersection T _{su of} the line L _U with the austenite phase range γ, is less than 50 ° C. The from the austenite region γ of the line L _U in the direction of the line L _O cut portion A _T thus provides the two-phase mixing region (γ + α) is enclosed tolerance range within which it is in the embodiment of the invention for the formation of pure Austenite may come.

By contrast, the line L _{O which} marks the upper limit of the sum "% Si + 2% Al" of the Si and Al contents of alloys processed according to the invention just touches the limit of the two-phase mixing range (γ + α) within which two-phase mixing structure occurs. Thus, each alloy according to the invention which has a value of its sum "% Si + 2% Al" lying between the lines L _U and L _O passes through the two-phase mixing range (γ + α) when it is cooled from an initial temperature below 1300 ° C. ,

To demonstrate the effect of the invention, two steels are S1 and S2 have been melted, their compositions in  Table 1 are given (data in% by mass, remainder iron and unavoidable impurities).

Table 1

The alloy of steel S1 is chosen so that the structure of steel S1 does not consist of pure austenite γ at any time when it cools down from 1300 ° C. In the case of steel S2, on the other hand, in the course of its cooling from the previously two-phase mixed structure γ + α for a temperature range T _{S of} less than 50 ° C, a purely austentic structure is formed for a short time, which immediately changes again into two-phase mixed structure γ + α when the temperature decreases further.

Steels S1 and S2 are cast into slabs which was then heated to a temperature below 1300 ° C however above the transition to two-phase mixing Range (γ + α) marking limit temperature for transition lying temperature have been reheated. At this The slabs each had a reheating temperature purely ferritic structure.

Then the slabs were roughed and in Framework from four different experiments 1 to 4 with a hot rolling start temperature in a seven roll stands  comprehensive hot rolling season entered, in which they too one hot strip has been rolled.

In trial 1, the hot rolling starting temperature was four slabs B1.1, B2.1, B3.1, B4.1 cast from steel S1 when entering the hot rolling season so high that the Steel is one made of austenite and ferrite Had two-phase mixed structure. In the hot rolling season are the slabs B1.1 to B1.4 accordingly initially in Two-phase mixing area has been rolled. The during the Rolling achieved in the two-phase mixing area was formed 40% and the degree of deformation in the ferrite area 66%.

This included rolling in the two-phase mixing area Rolling on the ferritic structure of the processed steel. In the course of this rolling in the ferrite area, a degree of deformation became reached by 66%. The finished from the slabs B1.1 to B1.4 hot-rolled hot strips left the hot rolling line a hot rolling end temperature ET and were at a Reel temperature HT coiled.

Table 2 shows the respective hot rolling end temperature ET in ° C, the reel temperature HT in ° C and the reel holding time tH in min as well as the magnetic properties P _1.5 for the slabs B1.1 to B4.1 or the hot strips produced from them in W / kg, J ₂₅₀₀ and J ₅₀₀₀ in T. In addition, Table 2 for the slabs B1.1 to B4.1 shows the degrees of deformation Ug γ / α achieved in rolling in the mixed region and the degrees of deformation Ug α achieved in rolling in the ferrite region.

Table 2, experiment 1

In experiment 2, the hot rolling starting temperature was this low that the five in turn cast from steel S1 Slabs B1.2 to B5.2 have a purely ferritic structure possessed after their structure in the course of their cooling had passed through the two-phase mixing range (γ + α). As a result, hot rolling is in the hot rolling season carried out exclusively in ferrite. It became a Overall degree of deformation Ug α of 80% reached. It is during of the second and third stitch with lubrication of the Band surface has been worked.

Table 3 shows the final hot rolling temperature ET in ° C, the reel temperature HT in ° C and the reel holding time tH in min as well as the magnetic properties P ₁ for the slabs B1.2 to B5.2 and the hot strips produced from them _{, 5} in W / kg, J ₂₅₀₀ and J ₅₀₀₀ in T.

Table 3, experiment 2

As in Experiment 1, the hot rolling start temperature was Test 3 so high that the cast from steel S2 Slabs B1.3, B2.3, B3.3, B4.3 when entering the Hot rolling mill is formed from austenite and ferrite Had two-phase mixed structure. In the hot rolling mill the slabs B1.3 to B4.3 are therefore initially in the Two-phase mixing area has been rolled. The one during this Rolling's degree of deformation Ug γ / α was 70%. To the Rolling in the two-phase mixing area included rolling ferritic structure of the processed steel. In the course of of this ferrite rolling, a degree of deformation Ug α of 33% reached.

Table 4 shows the respective hot rolling end temperature ET in ° C, the reel temperature HT in ° C and the reel holding time tH in min as well as the magnetic properties P _1.5 for the slabs B1.3 to B4.3 or the hot strips produced from them in W / kg, J ₂₅₀₀ and J ₅₀₀₀ in T.

Table 4, experiment 3

In experiment 4, too, the hot rolling starting temperature became the same chosen that the three slabs cast from steel S2 B1.4, B2.4, B3.4 when entering the hot rolling season Two-phase mixed structure formed from austenite and ferrite exhibited. In the hot rolling season, the slabs are B1.4 to B3.4 therefore also initially in the two-phase mixing area been rolled. In contrast to experiment 3 it was used  however a relatively low degree of deformation Ug γ / α of 40% respected.

This included rolling in the two-phase mixing area Rolling on the ferritic structure of the processed steel. In the course of this ferrite rolling, a degree of deformation Ug α of 66% achieved. The second and third took place Stitch with lubrication of the belt surface. The done hot-rolled hot strips left the hot rolling line a hot rolling end temperature ET and were at a Reel temperature HT coiled.

Table 5 shows the respective hot rolling end temperature ET in ° C, the reel temperature HT in ° C and the reel holding time tH in min as well as the magnetic properties P _1.5 for the slabs B1.4 to B3.4 or the hot strips produced from them in W / kg, J ₂₅₀₀ and J ₅₀₀₀ in T.

Table 5, experiment 4

Claims (17)

1. Non-grain-oriented electrical steel sheet or sheet with a nominal thickness of ≦ 0.75 mm, made from a steel which, in addition to iron, contains the usual unavoidable levels of impurities and optional levels of Mo, Sb, Sn, Zn, W and / or V, ( in mass%)
C: <0.005%,
Mn: ≦ 1.0%,
P: <0.8%,
Al: <1%
such as
Si with the stipulation 1.4% <% Si + 2% Al <2.5% (with% Si = Si content and% Al = Al content), the steel thus composed, as it cools down from a maximum of one Starting temperature of 1300 ° C, while restricting the temperature range in which an exclusively austenitic structure (γ phase) occurs in the steel during hot rolling, to a temperature range of less than 50 ° C passes through a temperature range in which it contains an austenite / ferrite Two-phase mixed structure (α-, γ-mixing phases), so that after hot rolling, pickling, cold rolling and annealing of the hot strip obtained after hot rolling, the electrical sheet has a magnetic polarization J measured in the longitudinal direction of the strip or sheet at a magnetic field strength of 2500 A / m ₂₅₀₀ ≧ 1.74 T and a value P _1.5 (50) of the magnetic losses of <4.5 W / kg measured in the longitudinal direction of the band at J = 1.5 T and a frequency f = 50 Hz. 2. Non-grain oriented electrical steel sheet or sheet according to claim 1, characterized in that its measured in the longitudinal direction magnetic polarization J ₂₅₀₀ ≧ 1.76 T. 3. A method for producing a non-grain-oriented electrical steel strip or sheet obtained according to one of the preceding claims, comprising the following steps:

• - Casting a steel which, in addition to iron, unavoidable impurities and optionally present levels of Mo, Sb, Sn, Zn, W and / or V, (in mass%) C: <0.005%, Mn: ≦ 1.0%, P: <0.8%, Al: <1% and Si with the requirement 1.4% <% Si + 2% Al <2.5% (with% Si = Si content and% Al = Al content) contains, to a preliminary product, such as a slab, a thin slab or a cast strip,
• - Processing of the preliminary product into a hot strip in a hot rolling process at hot rolling temperatures that are set starting from 1300 ° C so that a temperature range is passed through, with essentially complete exclusion of a purely austenitic structure (γ phase), in which the processed steel is an austenite / Ferrite two-phase mixed structure (α, γ mixed phases),
• - so that after a surface treatment comprising pickling, cold rolling and annealing of the hot strip obtained after the hot rolling process, the electrical steel strip or sheet has a magnetic polarization J ₂₅₀₀ ≧ 1 measured in the longitudinal direction of the strip or sheet at a magnetic field strength of 2500 A / m, 74 T and a value P _1.5 (50) of the magnetic losses of <4.5 W / kg measured in the longitudinal direction of the band at J = 1.5 T and a frequency f = 50 Hz,
• - The range of the temperature range within which the processed steel has a purely austenitic structure (γ-phase) is less than 50 ° C, and wherein the temperatures during the hot rolling process are bypassed this temperature range.

4. The method according to claim 3 or 4, characterized characterized that temperature of the preliminary product before the start of the hot rolling process up to 1150 ° C. 5. The method according to claim 4, characterized characterized that the at Hot rolling process reached final rolling temperature <800 ° C is. 6. The method according to any one of claims 3 to 5, characterized in that the reel temperature with which the hot strip after Hot rolling process is rolled up, <650 ° C.   7. The method according to any one of claims 3 to 6, characterized in that the hot rolling process in one of several rolling stands comprehensive hot rolling series of final rolling includes. 8. The method according to claim 7, characterized characterized that the in the course of the Final rolling achieved total forming degree <75%. 9. The method according to claim 8, characterized characterized that the in the course of the Final rolling achieved in the two-phase mixing area Degree of deformation <45%. 10. The method according to claim 8, characterized characterized that the in the course of the Final rolling achieved in the two-phase mixing area Degree of deformation is at least 35%. 11. The method according to claim 7, characterized characterized that the final rolling only at temperatures in which the each processed steel exclusively a ferrite Has structure. 12. The method according to claim 7 and one of claims 10 or 11, characterized in that the processed with ferritic structure Steel's hot rolling passes with lubrication respectively.   13. The method according to any one of claims 3 to 12, characterized in that the hot strip in the course of its surface treatment which is mechanically descaled. 14. The method according to any one of claims 3 to 13, characterized in that the cold strip obtained after cold rolling Is subjected to annealing in a continuous furnace. 15. The method according to claim 14, characterized characterized that the glow in in a non-decarburizing atmosphere. 16. The method according to any one of claims 3 to 13, characterized in that the cold strip obtained after cold rolling Is subjected to annealing in a bell annealer. 17. The method according to any one of claims 14 or 16, characterized in that the annealed strip with a degree of deformation <12% postformed and then a reference annealing at Subjected to temperatures above 700 ° C so that an annealed electric fire is obtained.